Mass antimicrobial administrations have been used to combat parasitic diseases such as onchocerciasis, filariasis, and malaria with varying success and have been proposed for a variety of bacterial diseases. The World Health Organization (WHO) has initiated a comprehensive program to eliminate blinding trachoma, in large part based on the mass treatment of entire trachoma-endemic communities with oral azithromycin. Repeat treatment will almost certainly be necessary, but we do not know whether infection can be eliminated--the common wisdom is that it cannot. Mathematical models imply that elimination is possible but only under certain conditions. Our preliminary results in Ethiopia suggest that these conditions are present but will need to be tested empirically. Models also imply that children form a core group for the transmission of trachoma--if infection can be eliminated in this age group then it would presumably fade away in adults, whose treatment now requires a substantial portion of a program's resources. This strategy also needs to be tested in a hyper-endemic area such as Ethiopia. A bacterial disease has NEVER been eliminated by mass antibiotic distributions. If ocular chlamydial infection can be eliminated by repeat antibiotic treatment of only a subgroup of the population, then this will not only provide a rationale for trachoma programs, but also may provide a valuable strategy against a variety of bacterial scourges. Specific Aim 1. To determine whether mass treatments can eliminate ocular chlamydia from the most hyper-endemic communities. Will biannual repeat treatment be sufficient to reduce ocular infection in a community to zero? Specific Aim 2. To determine whether children form a core group for the transmission of trachoma. Can treatment targeted to children alone eventually eliminate infection in the entire community?